EVAPORATION 379 at the rate of 0.7 gal. per square foot. Quantities are usually small and only single effects are used. Evaporators of cast iron, tubes of aluminum. Sodium Phosphate.—Solutions are concentrated from 6 to 24 per cent in a horizontal-tube double-effect evaporator with a steam pressure of 5 Ib. and a vacuum of 26 in., at the rate of IK gal. per square foot. Evaporators are of cast iron or steel, with tubes of steel. Sodium' Silicate.—Concentrated from 50 to 60 per cent in a horizontal-tube single effect with a steam pressure of 5 Ib. and a vacuum of 26 in., at the rate of M to K gal. per square foot. Evaporators are built of cast iron with steel tubes. Capacity per square foot of heating surface is very low on account of the heavy coating of the tubes. Sodium Sulphate.—The saturated solution of from 30 to 33 per cent solids is concentrated in single or multiple-effect evaporators of the vertical-tube type, with a steam pressure of 5 Ib. and a vacuum of 26 in., at the rate of from 1 to \Y± gal. per square foot. The sodium sulphate is recovered in salt filters, and a rapid circulation between evaporator and salt niters must be maintained in order to prevent heavy coating on the tubes. Sodium Sulphide.—Concentrated from 8 to 45 per cent in single or multiple-effect evaporators of the horizontal-tube or rapid-circulation type, with a steam pressure of 5 Ib. and a vacuum of 26 in., at the rate of IK to 2 gal. per square foot. Evaporators are of cast iron with tubes of charcoal iron or steel. Sometimes the liquor is further concentrated to 60 per cent in the Mantius high co"™"4"™*"1'' which is equipped with cast-iron tubes. Sulphuric Acid.—Weak acid solutions are successfully concentrated in multiple-effect evaporators of the vertical-tube or horizontal-tube type, having cast-iron shells and lead lining, with lead tubes; in some cases the whole apparatus is built of lead. Capacity, steam pressure and vacuum depend on special conditions. ORGANIC PRODUCTS Sugar, Glucose and Maltose.—One ton of sugar cane will give about 150 Ib. of sugar in Louisiana, and from 200 to 225 Ib. in the tropics. The juice will amount to 200 gal. per ton, with a density of from 5K to 8°Brix. It is concentrated in a triple or quadruple-effect evaporator to about 27°B6., with a steam pressure of 10 Ib. and a vacuum of from 27 to 28 in. The capacity is 3 to 4 gal. per square foot, and the Standard, Lillie, Kestner, Sanborn and Swenson evaporators are the usual types. The 27°B6. solution is concentrated to 42° in single effects of the coil or Standard type. The capacity is about 1 gal. of water evaporated per square foot, and either live or exhaust steam is used in these pans. Beet Sugar.—One ton of beets will give about 1M ton of juice, having a density of from 7 to 8>i°Bd. The concentration is done in two stages, and triple- or quadruple-effect evaporators with a capacity of from 3 to 4 gal. per square foot are used for the concentration up to 27°B6. The Wellner Yelinek, Swenson and Kilby construction are the usual types. The final concentration up to 42°Be'. is done in single effects of the coil or Standard type, with a capacity of about 1 gal. per square foot.